Hydraulic circuit with dual pressure control



March l, 1949. M, W HUBIER 2,462,971

HYDRAULIC CIRCUIT WITH DUAL PRESSURE CONTROL Y (Ittotnegs March 1, 1949. M, w HUBER HYDRAULIC CIRCUIT WITH DUAL PRESSURE coNIRoL 2` sheets-sheet 2 Filed May 8, 1947 @Q @Q Lv:

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HYDRAULIC CIRCUIT WITH DUAL PRESSURE CONTROL Matthew W. Huber, Watertown, N. Y., assigner to The New York Air Brake Company, a corporation of New Jersey Application May 8, 1947, Serial No. 746,755

This invention relates to hydraulic 'circuits and particularly to control mechanism arranged to operate the circuit under high head pressure when there is a demand for hydraulic liquid and relatively low head pressure at all other times. The system was developed for use on airplanes and since this iield of use imposes peculiarly difficult requirements, which are met by the invention, the concept will be described as so used.

It is usual practice on large bombing planes and cargo planes to operate secondary mechanism, such as landing gear, aps, tail surfaces and the like, hydraulically. The hydraulic pressure is developed by a pump or pumps driven by one or more of the propelling engines. As a consequence, the pump must run continuously when the plane is in flight. Since the capacity of such a pumpis limited and `since weight considerations dictate the use of the smallest practicable motors, it is necesary to operate the pumps at high speed, for example, from 2500 to 3500 R. P. M. and to develop high head pressures, for example, r000 P. S. I.` It is very diiiicult to keep a hydraulic circuit tight under a continually maintained pressure of 3000 pounds, and particularly so under the conditions of severe vibration encountered in an airplane.

In a prior application, Serial No. 626,690 filed November 5, 1945, now Patent Number 2,433,222, there is described a parallel cylinder pump of the variable displacement type in which displacement is-controlled in response to head pressure. This pump has very good control characteristics in that it will deliver its maximum capacity or approximately its maximum capacity until the desired limiting pressure is closely. approached and then reduce its displacement very rapidly. Because of these desirable characteristics, this particular pump is chosen for illustration. The pump itself is not a, feature of the present invention and is not claimed herein. Itis expressly recognized that other variable displacement pumps could be substituted without changing the basic principle.

According to the present invention, a shiftable controller which varies the displacement of the pump is operated by a, regulator in the form of an expansible chamber motor, subject to the discharge` pressure developed by the pump and acting on the controller in a direction to reduce the delivery rate of the pump. The controller sets the pump for any delivery rate between full delivery and zero. Since the maximum discharge pressure of the pump is high, the effective area of the regulator motor is very small. This motor is loaded in a direction to increase pump delivery by yielding means which take the form of a coil compression spring. This spring is sustained by 'an adjustable seat which takes the form of a piston whose effective area is many times that of' 10 Claims. (Cl. 60-97) the regulator motor. This piston is shiitable between two limiting positions in one of which the piston spring seat is not under pressure and the delivery of the pump is controlled to maintain a relatively lowdelivery pressure and in another of which the piston spring seat is under pressure and the delivery of the pump is controlled to maint-ain the standard value, say 3000 p. s. i. The piston spring seathas a bleed port so that pressurel acting upon it in a direction to set the controller for high delivery pressure tends to bleed away unless continuously replenished. The delivery line of the pump is connected to a control valve or control valves controlling one or more accessory hydraulic motors and the piston spring seat is in communication with said accessory motors in such a way that when any accessory motor is under pressure, the piston spring seat is also under pressure and will move to establish high pressure delivery. When all the motors are vented, the pump is set for low pressure delivery. Thus the shiftable spring seat functions in response to pressure to select the delivery pressure at which the pump operates. It will hereafter be referred to as a pressure responsive selector.

This scheme requires a pilot line between the piston spring seat and each motor. A simple ,arrangement of check valves is used to prevent iiow from one motor to the other. Since the piston spring seat is of large area, as compared to the regulatory motor, it is possible to have a very wide spread between maximum and minimum delivery pressures. For example, a pressure as low as pounds is suilicient to shift the piston spring seat full stroke, and thus effect the desired selection.

Sometimes an airplane having several motors will require the use of certain motors which operate under high pressure only occasionally but will `also require the use of other motors which are operated under lower pressures and at very frequent intervals. 4The invention permits an arrangement in which the lower pressure is available continuously and the high pressure only when a high pressure motor is being operated. For example, the system can be caused to develop 1500 pounds continuously and 3000 pounds on demand.

Practical embodiments will be described with reference to the accompanying drawings. Figure 1 is an axial section of a parallel cylinder pump showing the control mechanism together with a hydraulic circuit including the pressure controlling pilot line, said circuit being drawn in minature as compared with the pump,

`to permit the control mechanism of the pump shownjas they wouldappear when there is a dev mand for high pressure iluid andthe pump isA4 conditioned to operate at full capacity.

Figure 2 shows a view similar to Figure 1, but

illustrating a modified construction designed to operate continuously at a moderate pressure, say 1500 p. s. i. and when there is a demand for high pressure iluid to operate at high pressure.

say 3000 p. s. i. The controller of the pump is shown set to maintain high pressure. In'this view, two of the motors included yinthe hydraulic circuit are of the type which never operates above 1500 11.5.1. 1

Refer rst to Ffigure l. The main housing of the pump is shown'at 6 and the head at 41. The pump chosen for illustration has nine plungers whichare parallel and which are reciprocated by a swash plate, not visible in the drawing. One

plunger 8 appears in elevation and another plunger 8 is shown in section. These plungers work in cylinder bores in a cylinder block 9. Each plunger controls an inlet passage and discharges oil through a spring-loaded discharge valve I2, of which there are nine, one for each cylinder and plunger.

The suction connection to the pump is indicated at |3 and communicates by passage |4 and port I5 with the intake ports I of all the cylinder bores.

Each plunger 8 is counterbored at its outer end, as indicated at I6, and the counterbore leads to radial ports I1. The ports I1 are controlled by regulatory valves I8 which encircle respective plungers and are shiftable in unison in the direction of the axesof the plungers by a spider I9. When the regulatory valves I8 are in the full displacement position shown in the drawing, the ports I1 are blanked by the regulatory valves |8 just as the end of the plunger 8 overtravels the edge of its inlet port II. quently, the displacement of the pump is at its maximum. As the valves I8 are moved further and further to the right (with reference to Figure l) the eiective stroke of the pump plungers is reduced because the ports |1'1'emain open after the end of the plunger 8 has over-travelled the edge of the inlet port II.

The spider I9 is mounted on a rod 2| which is lslidable in a path parallel with the axis of the pump plungers 8. It is guided in the cylinder bushing-22 xed in the center of the cylinder -pressure developed in the passage 24 urges the rod 2| to the right. The effective area of the piston 23 is the difference between its cross sectional area and the cross sectional area. of the rod 2| where the rod enters the cylinder bushing. vObviously this effective area is quite small. It must be small because the maximum pressure developed by the pump is high and it is not desirable to use a very heavy loading spring. A choke 21 is interposed in passage 26 to prevent the piston 23 from responding to such high frequency pressure pulsations as may exist in the passage 24.

To the right o: piston za an extension of rod 2| forms` a head 28 on which is mounted a thimble-shaped spring seat (23. Spring seat 23 is connected by a bolt 3|l with a thimble-shaped spring seat 35. An intermediate spring seat 32 is slidable on bolt 3| and sustains the proximate endsy of two springs 33 and 34, arranged in tandem 'between the spring seats 23 and 35. This arrangement facilitates assembly of the springs under initial stress and resists lateral deection such as might occur with a single spring of the same overall length.

The mechanism so far described is basically similar to that described in the prior pump application above identiiled. The present invention adds. among other things, a pressure operated means for changing the regulating action of the springs 33 and 34. K

Threaded into the end of the cap 1 is a motor housing 36, tubular in form and internally threaded at its outerk end. Threaded into the outer end is an internally shouldered cylinder bushing 31. A cap 38 is threaded on to the projecting end of the cylinder bushing, the construction being such that the cylinder bushing can be adjusted axially inthe housing 36 and then locked in place by the cap. The purpose of this is to permit adjustment of the position of shoulder 38 in the cylinder bushing. The position of -this shoulder determines the maximum pressure setting of the pump controller and consequently requires adjustment. Leakage is precluded by conventional gaskets 4| and 42 which lare mounted in grooves, as shown in the.

sion spring 45. The spring seat 35 ts on the end of the piston 43 and is sustained thereby, A bleed port 46 permits a metered leakage through the piston 43 from the space at the outer (righthand) end of the piston through the clearance aroundV bolt 3|, where it passes through spring seat 35, tothe passage I4 and consequently to the inlet or lowpressure side of the pump. The pilot line 41 is connected to cap 38 so that whatever pressure exists in the pilot line 41 reacts on the outer right-hand end of piston 4 3.

When piston 43 is forced to the left, head 44 engages shoulder 39, and springs 33, 34 acting in tandem are stressed to develop an appropriate spring loading. This loading opposes discharge pressure which urges piston 23 to the right. When the supply of pressure fluid to the pilot line 41 is cut olf, hydraulic pressure at'the right of piston 43 will bleed away at a controlled rate through port 46. Consequently, the piston 43 will move outward andthe loading springs 33 and 34 will be no` longer rigidly sustained by the piston 43.

As a practical matter, the loading function is transferred to the spring 45 which is comparatively weak. Whether the springs 33 and 34 operate as a rigid connection depends on the minimum stress imposed on these springs by bolt 3|, but in any case they approximate that condition so that to allintents and purposes the loading of the pump is determined by the light spring 45. 'Ihis is so chosen that the pump will operate at a low pressure, say pounds. The precise pressure is not important, provided it is low, and always provided that it is high enough to force piston 43 to its limit of motion despite the resistance oiered springs 33 and 3,4. The point Just mentioned is significant. The lowest discharge pressure developed by the pump should be capable of shifting the pressure control to the high pressure setting.

Discharge line 25 leads to a series of control valves 48. These are illustrated conventionally as three-way valves, each of which has one connection to the high pressure line 25, a second connection to discharge line 48 which leads to the low pressure sump 5|, and a controlled connection 52 which leads to a motor 53. These motors are here illustrated as simple single acting displacement motors, but so far as the invention is concerned, it is immaterial what type they are. They can be any consumer of pressure fluid.

Each valve 48 connects its related motor 53 selectively to supply line 25 or to discharge line 49.

According to the invention, the valve 48 should also connect pilot line 41 to the high pressure line 25 whenever it connects the related motor 53 to the high pressure line. This could be done in various ways but the simplest way is to connect the line 41 directly `to the branch 52. It is necessary to prevent the pilot line 41 from connecting each motor 53 with another or others. The simplest arrangement to produce this result is to interpose, in each connection, a check valve 50 opening away from the branch 52. Because of the use of these check valves, the .valve 48 cannot function to vent the line 41. It is this circumstance that leads to the use of the bleed port 46 but there are incidental-advantages in its use.

Unless pressure fluid is continuously supplied to the line 41, the pressure acting inward on the y piston 43 will bleed away through the port 46. Whenever any of the motors 53 is under pressure, pressure is maintained in the pilot line 41 despite the bleeding action of the port 46. However, if all the motors are exhausted, the pressure iluid which had forced piston 43 to the left, bleeds away at a rate which can be selected by choosing an appropriate capacity for the port 46. Thus the part 43 is a pressure-responsive selector and functions to select between two different delivery pressures.

The rst and second of the row of valves 48 are shown set in exhaust position. The third is set in supply position. Consequently, in Figure 1, the line 41 is under pressure and the pump is set to maintain 3000 pounds. If the third valve 48 be turned from the position shown to release position, all other valves 48 remaining in release position, the pressure in line 41 will bleed away and the piston 43 will move to the right, transferring control from the springs 33, 34 to the light spring 45. Experience has shown that the discharge pressure of the pump .falls gradually over a period of several seconds. `If any of the valves 48 -be then moved to supply position, the pressure in the line 25 will rise to 3000 pounds in a fraction of a second, but the response of the control is so sensitive that the 3000 pound pressure is reached without hydraulic shock:

The high pressure is attained before the motorl 53 has moved full stroke and the demand for liquid which is then continuing and the assumption of load by the motor are suicient to inhibit any serious shock eiect. Since a suddenly applied load produces much more severe strains than does a slowly applied load of the same magnitude, the importance o! this characteristic is obvious.

scribed in Fig. 1 are given the same reference numeral, increased `by 100, so that in discussion of the two embodiments, no confusion can occur,

while detailed description can be minimized.

So far as the pump is concerned the essential differences are 1. There is no spring corresponding to spring 45 of Fig. 1.

2. Piston |43 can move between the position shown in which head |44 engages shoulder |38 (high pressure setting) and a position in which head |44 engages the cap |38 (low pressure setting).

3. Bolt |3| is rmade long enough to allow spring seat |35 to move through the described range.

4. Springs |33, |34 are so chosen as to strength and scale that, in high pressure setting of pressure-responsive selector |43, they control at the desired high pressure, here assumed to be 3000 p. s. i. and, in low pressure setting, they control at the desired low pressure, here assumed to be 1500 p. s. i.

In short, where the spread between high and low pressure is too great to be effected by adjusting the spring unit, control can be transferred to a lighter spring as is indicated in Fig. 1. Where the spread is not too great the construction of Fig. 2 is preferred because simpler.

As to the circuit, the only differences in Fig. 2 as compared to Fig. 1 arise from the optional presence of additional motors which operate at 1500 p. s. i.

There is a supply line |25, exhaust line |49, sump |5|, two valves |48`and two motors |53. For each of these motors there is a check valve |50 controlling connection to pilot line |41. These parts ail function in the manner described as to similarly numbered parts in Fig. 1. i

The additional motors are indicated at 55. They are controlled by three-way valves 56 similar to valves |48 and similarly connected to exhaust line |49. These valves are fed with liquid at 1500 p. s. i. by line 51 which is fed from line |25 by a pressure reducing valve 58.

Valve 58 is of the type which controls in response to pressure on its discharge side. when line |25 is at 1500 p. s. i. valve 58 simply opens Wide. When pressure in line |25 is above 1500 p.A s. i. valve 58 functions to limit pressure in line 51 to 1500 p. s. i.

Motors 55 are not connected to pilot line |41, and can bev operated at 1500 p. s. i. while the system is operating at that pressure, or while a motor `|53 is operating at 3000 p. s. i. r

The pump mechanism is not claimed herein but forms the subject matter of my Patent No. 2,433,222 and my application Serial No. 757,621, led June 27, 1947.

1. The combination of a displacement pump including a shiftable controller for varying between zero and full capacity the displacement of the pump; means responsive to the pressure of liquid delivered by the pumpand" arranged to shift said controller'in response to` rising delivery pressure in a direction to reduce pump displacement; adjustable loading means serving to resist such shift; at least one motor device operable by liquid delivered by said pump; a valve operable to connect said motor device vselectively with Thus,

pump discharge or with exhaust; and pressure' responsive means subject toV pressure in said Ymotor device and serving to adjust said loading means to maintain a low'but positive discharge pressure when themotor device'is exhausted and Y maintain maximum discharge pressure when said motor device is under pressure.

2. The combination of a variable displacement pump; a controller shiftable to vary the delivery rate of said pump between zero and a maximum: a regulatory motor responsive to the ,delivery pressure developed by said pump, urging said controller toward its zero setting; spring means capacity of said restricted vent only when said.

valve delivers liquid to said consumer.

3. The combination deined in claim 2 in which the loading motor is a piston, and the spring means ycomprises a heavy spring -for regulating at high pressure and a light springl for regulating biasing said controller in the opposite direction;

a loading motor shiftable to load said spring means to cause the pump to deliver against a high back pressure, said loading motor having a restricted vent, and being shiftable by the spring means, when vented, to load the controller lightly so as to cause the pump to suspend delivery when opposed by a low but positive back pressure; a valve controlling the supply of liquid pumped by the pump to a consumer of-pres sure liquid; and a flow connection of a flow capacity materially exceeding that of said restricted vent from said consumer to said loading motor.

5. AThe combinationdeiined in claim 4 in which there are a plurality of consumers of pressure liqui d and valves respectively controlling the consumers, and in which all the consumers are connected with the loading motor but are isolated from eachother by check valves interposed in said connections.

6. The combination of a variable displacement pump; a controller shiftable to vary the delivery rate of said pump between zero and a maximum; a regulatory motor responsive to the delivery pressure developed by said pump and serving to urge said controller toward its. zero delivery setting; spring means biasing said controller in the opposite direction; a loading motor, which when subjected to pressure, loads saidspring means to cause the pump to deliver againsta high'pressure, and vwhen vented reduces the loading on said spring to cause the pump to suspend delivery when opposed by a lower pressure; a supply line connected with the discharge of said pump; aA

pressure motor selectively with said exhaust line or with said supply line; a connection-for sub' iecting said loading motor to the pressureestablished in the high pressure motor by the opera` tion of said valve; a second` supply line; a pressure reducing valve for supplying liquid to the second supply line from the rst supply line at a pressure aproximating said lower pressure; at least one low pressure motor and a valve operable to connect said low pressure motor selecitively with the second supply line or with the exhaust line.

7. The combination of a displacement pump having pressure operated'means for reducing the displacement'of the pump to zero in response to attainment of an established limiting dischargel pressure; a pressure responsive selector for establishing alternatively two dii'erent limiting discharge pressures; a motor operable by :pressure liquid delivered by the pump; a valve for connecting said motor selectively with the pump discharge or with exhaust; and a connection between said selector and said motor, the parts being so arranged that the selector establishes the lower of said two limiting pressures when the motor is connected to exhaust.

8. The combination deilned in claim '1 in which there is a restricted vent from the selector, there are at least two motors each controlled independently by a corresponding valve; and all motors are connected with the selector by a connection having a flow capacity which materially exceeds that of said restricted vent but are isolated from one another by check valves, whereby the selector will establish the lower limiting pressure when all motors are connected to exhaust.

9. The combination of a displacement pump including a shiftable controller for varying between reduced and full capacity the displacement of the pump; means responsive kto the pressure of liquid delivered by the pump and ar ranged to urge said controller in the direction to reduce pump displacement; two spring means differing in strength and each arranged to oppose said pressure responsive means; a spring seat shiftable between two positions in which respectively it causes one or the other of said spring means to oppose said pressure responsive means and thus establish high and low discharge pressure settings; a pressure motor serving when subject to discharge pressure to shift the spring seat to establish the high pressure setting; and means including a valve operable alternatively to subject said motor to the discharge pressure developed by the pump and to free it therefrom.V

10. The combination defined in claim 9 in which the pressure motor stresses the high setting spring as it moves to establish the high discharge pressure setting; and an adjustable st op is provided to limit such motion of the motor.

MATTHEW W. HUBER.

REFERENCES CITED The following references are of record in the file of this patent: s

UNrrED vs'rA'riizs'-Prl'rnN'rs Number 

